Spectroscopic implications of partially quenched orbital angular momentum in the OH-water complex.

The OH monomer orbital angular momentum is predicted to be partially quenched in the OH-water complex because of the significant splitting of the OH monomer orbital degeneracy into (2)A' and (2)A' ' electronic states. This orbital angular momentum quenching and the associated decoupling of the electron spin from the a inertial axis are shown to have dramatic effects on the rotational band structure of the microwave and infrared transitions of the OH-water complex. At the ab initio values for the splitting between the (2)A' and (2)A' ' surfaces, simulated spectra of a- and b-type bands, such as those expected for the OH radical stretch and water asymmetric stretch, are predicted to have a noticeably different appearance than the well-established limiting cases associated with fully quenched or completely unquenched orbital angular momentum. Spectral identification of the OH-water complex in the gas phase will require explicit consideration of this quenching phenomenon.